Novel Gel Phase: A Cubic Phase of Densely Packed Monodisperse, Unilamellar Vesicles

A novel type of gel phase has been investigated in the ternary surfactant system sodium oleate/octanol/water. It occurs at relatively high octanol content (molar ratio of ∼2:1 for octanol/oleate) and for a total concentration of amphiphile in the range of 5−15 wt %. This phase is transparent, isotropic, and highly viscous and possesses elastic properties (“ringing gel”). Microstructural investigations by means of freeze-fracture electron microscopy and small-angle neutron scattering show that it is mainly composed of small unilamellar vesicles. The observed size is also in good agreement with the measured rheological properties. These vesicles are remarkably monodisperse and form a highly ordered phase (presumably of cubic type); i.e., this is the first time that such a liquid crystalline array of vesicles has been observed.